Hot gas valves are known from DE 10 2007 000 217 A1 and US 2007/0095334 A1. These are EGR valves with a housing in which a gas duct with an inlet and an outlet is formed, and with a valve device, constructed as a flap, for controlling the fluid flow through the gas duct. The housing has a cooling duct for liquid cooling of the housing. The gas duct is shielded with respect to the housing by a thermal shield, which consists of a material which has a greater thermal stability/resilience than the material of which the housing consists. The valve device has a closure body situated in the gas duct, which is held on a valve shaft mounted rotatably in the housing by means of a bearing. In the hot gas valve known from DE 10 2007 000 217 A1, the housing is an aluminum pressure die casting product, and the shield is formed by a housing protection element, designated as a nozzle, for protecting a wall surface which defines the fluid duct in the housing. The hot gas valve is intended to be suitable for exhaust gases which have a higher temperature than 500° C. The housing protection element consists of a heat-resistant material, such as e.g. a high-grade steel or a heat-resistant steel. The bearing is formed by a metallic bushing which is not specified in further detail, or by a sintered oil bearing.
Despite the thermal shielding of the gas duct which is provided with respect to the housing, in the case of high fluid temperatures above 500° C. often an unacceptably high introduction of heat into the housing occurs, so that in particular a drive for the valve shaft arranged in or directly at the housing and containing electrical and electronic components is exposed to unacceptably high temperatures.
From WO 2008/144686 A1 a substantially similar hot gas valve is known without cooling ducts serving for liquid cooling of the housing, in which the valve shaft is mounted by a ball bearing or by a metal ring containing bronze and Teflon.